Temperature sensor for tracking body temperature based on printable nanomaterial thermistor
Provided are wireless temperature sensors. A temperature sensor with a flexible, large-area printed thermistor can include an negative temperature coefficient (NTC) thermistor for temperature sensing, a control circuitry for electrically connecting with the NTC thermistor and obtaining the temperature sensed by the NTC thermistor, a power source for providing power supply to the NTC thermistor and the control circuitry, and a frame element for supporting the NTC thermistor, the control circuitry and the power source, where the frame element is at least partially thermally insulated to establish thermal equilibrium within the temperature sensor. The temperature sensor can sense the temperature in a fast and accurate way due to fast thermal equilibrium established within the sensor.
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This disclosure generally relates to a thermometer field, and particularly to temperature sensors for tracking body temperature based on printable nano-material technology.
BACKGROUNDSmart/wearable devices for body temperature tracking are becoming more and more challenging based on traditional temperature sensing technologies. Electronic sensors for temperature are typically composed of tiny tips of negative temperature coefficient (NTC) ceramic materials, platinum (PT-100) or infrared photo-devices. These electronic sensors don't have enough accuracy for temperature sensing when becoming wearable on a human body since the thermal contact area is limited. It is challenging for these sensors to build up thermal equilibriums with the human body under ambient environments, and thus these thermometers take a very long time to measure the body temperature, such as 10-15 min or much longer. There are also some flexible thin films of platinum sensors for temperature but their area is limited to 1 mm-2 mm since Pt is quite expensive. Therefore, it is very difficult for traditional sensors to continuously monitor and track physiological signals as smart/wearable devices, especially when biometric information on the human body almost changes every second.
SUMMARY OF THIS DISCLOSUREIn one aspect, a temperature sensor based on a printable thermistor can include an negative temperature coefficient (NTC) thermistor for temperature sensing, a control circuitry for electrically connecting with the NTC thermistor and obtaining the temperature sensed by the NTC thermistor, a power source for providing power supply to the NTC thermistor and the control circuitry, and a frame element for supporting the NTC thermistor, the control circuitry and the power source, where the frame element is at least partially thermally insulated to establish thermal equilibrium within the temperature sensor.
The NTC thermistor may include a substrate, a Si—C film printed on the substrate, and electrodes printed on the substrate for electrically connecting the Si—C film with the control circuitry. The NTC thermistor may also include a first laminate arranged on the Si—C film and the electrodes, and a second laminate arranged on a top surface of the first laminate for preventing moisture from penetrating into the NTC thermistor.
In some embodiments, the control circuitry may include a constant current driving circuit which connects with the electrodes of the NTC thermistor. The constant current driving circuit can drive the NTC thermistor with a constant current at a low bias. In this case, the current passing through the NTC thermistor can be kept constant, and thus its operation temperature can be substantially controlled within an allowable range, thereby greatly avoiding a degradation of crosslinking of polymer binders between Si and C nanoparticles within the Si—C film and ensuring a film quality of the printed Si—C film.
In another aspect, a wireless temperature sensor can include an NTC thermistor for temperature sensing, a control circuitry for electrically connecting with the NTC thermistor and obtaining the temperature sensed by the NTC thermistor, a wireless module for receiving the temperature from the control circuitry and sending out the temperature in a wireless way, a power source for providing power supply to the NTC thermistor, the wireless module and the control circuitry, and a frame element for supporting the NTC thermistor, the control circuitry, the wireless module and the power source, where the frame element is at least partially thermally insulated to establish thermal equilibrium within the temperature sensor.
The NTC thermistor may include a substrate, a sensing element, an internal laminate and an external laminate arranged successively. The sensing element can include a Si—C film and electrodes printed on the substrate, where the electrodes connect the Si—C film with the control circuitry. The internal laminate may have a WVTR of substantially 1-100 gam/m2/day and the external laminate may have a WVTR of below substantially 0.1 gram/m2/day, such that the NTC thermistor is prevented from moisture penetration.
The control circuitry can include a constant current driving circuit for driving the NTC thermistor with a constant current, and a measurement circuit for sampling a sensed voltage outputted through the electrodes of the NTC thermistor. The sensed voltage is determined based on the constant current and a resistance of the NTC thermistor.
Various embodiments of this disclosure can provide temperature sensors based on a printable thermistor. The temperature sensors can be configured with excellent thermal insulation, thereby enabling fast and accurate tracking of a body temperature when the temperature sensor is attached to a human body.
Following detailed descriptions of respective embodiments in this disclosure can be understood better when combining with these figures, in which the same structure is represented by the same reference sign. In the figures:
Below this disclosure will be fully described in detail with reference to various embodiments and accompanying drawings.
Temperature sensors (which may also be named as thermometer) for body temperature tracking are provided in various embodiments of this disclosure. Temperature sensing element including silicon-carbon nanocomposite materials may be fabricated into a printed thermistor by printed nanoparticle technology, in order to accurately and fast measure human body temperature. Hybrid laminates with low WVTR and high WVTR can be used to encapsulate the printed thermistor, so as to obtain both optimum curing conditions for printed films and a better lamination for moisture barrier. The temperature sensors can have conformal contact to human skin surface for large-area temperature sensing. Thermal insulation can be formed for the temperature sensor on a backside facing away from the human skin surface, such that fast thermal equilibrium is able to be built up within the thermometer and the sensing for body temperature can be as fast as substantially 1-2 seconds. The thermometer can also be provided with a constant current (CC) driving circuit to control an operation temperature of the printed thermistor.
As shown in
Here, the frame element 24 can be at least partially thermally insulated to establish thermal equilibrium within the temperature sensor 200. The frame element 24 can be thermally insulated itself, and/or a thermal insulation structure can be attached onto or embedded within the frame element 24 to establish the thermal equilibrium. The thermal insulation can be enabled for the whole frame element 24; alternatively, one side or one portion of the frame element 24 can be designed to have thermal insulation. In an example, at least the front side 241 and/or the back side 242 of a portion of the frame element 24, for example a portion for arranging the NTC thermistor 21, can be thermally insulated. Due to the thermal insulation configuration, fast thermal equilibrium is able to be built up between the whole thermometer 200 and the human body, and the sensing for body temperature can be as fast as substantially 1-2 seconds. The materials used for thermal insulation may include polyethylene terephthalate (PET), polypropylene (PP), polyethylene (PE), polyvinyl chloride (PVC), polytetrafluoroethylene (PTFE), or other plastics, or some soft rubber sheets with thickness of substantially 0.5 mm-1 mm.
Further referring to
Silicon and carbon nanoparticles (NPs) are relatively stable under ambient environments, but the temperature sensors based on Si—C NPs need to be encapsulated good enough to prevent moistures from permeating into core devices. Moreover, when flexible temperature sensors work as wearable thermometers, skin moisture is also needed to be prevented from permeating through a surface barrier film in a skin contact area. For this reason, the materials with excellent moisture prevention can be used to fabricate the substrate 211. Also, since the temperature sensor 200 is worn on the body surface, the biocompatibility should be considered as well. In an example, the substrate 211 can be preferably made of liquid-crystal-polymer (LCP), or an LCP film can be preferably used as the substrate 211, due to high interfacial adhesion, biocompatibility, and extremely low degree of moisture absorption of the LCP. Its biocompatibility makes LCP encapsulated sensor be stable on a skin surface and insensitive to human skin, and its moisture barrier property can be defined as a water vapor transmission rate (WVTR) of substantially 0.01 gram/m2/day. In some examples, another laminate, such as an Al foil, can be laminated on an outer surface of the LCP film to further improve the moisture prevention function of the NTC thermistor 21.
The hybrid laminate arranged on the Si—C film 212 and the electrodes 213 can encapsulate the NTC thermistor 21 from a top orientation, and can simultaneously have high and low WVTRs. That is, the Si—C film 212 and the electrodes 213 can be arranged between the substrate 211 and the hybrid laminate. The hybrid laminate can include an internal laminate 214 and an external laminate 215, where the internal laminate 214 is intermediate between the sensing element and the external laminate; i.e., the external laminate 215 and the sensing element are arranged on two opposite sides of the internal laminate 214. In the orientation shown in
In an example (
In another example, some other laminate, such as an Al foil, can also be laminated on an outer surface of the external laminate to further improve the moisture prevention function of the NTC thermistor 21.
Referring to
It is already known that the printed Si—C NPs temperature sensors 100 and 200 may work as negative temperature coefficient (NTC) thermistors. When the NTC thermistors are used for temperature measurement, they may connect to a corresponding measurement circuit. Most frequently, the measurement circuits are voltage dividers or bridge circuits (such as a Wheastone Bridge). However, due to strong nonlinearity of the thermistor characteristic, which is of an exponential type, when the temperature sensor is driven by a Wheastone Bridge, constant voltage (CV) can be applied across the printed Si—C NPs film and with applied voltage fixed, currents passing through the Si—C NPs may increase over one order of magnitude from room temperature to around body temperature. High currents at high temperature will potentially induce additional heating and charging effects within thermistors, and degrade the crosslinking of polymer binders between Si—C NPs and the film quality of the printed Si—C NPs. Therefore, there is the requirement to control the current in a readout system for resistance temperature detectors, in order to extend its operation temperature range.
For the purpose of current control, a constant current driving circuit 221 can be provided in the control circuitry 22, so as to drive the NTC thermistor 21 with a constant current. A schematic design for a CC bias mode can be found in
Under the action of the constant current, the sensed result that is read out from the NTC thermistor 21 can be highly dependent upon its own resistance, which is further determined according to the temperature of the user's body surface. Specifically, the NTC thermistor 21 may generate a sensed voltage varying with the sensed temperature as follows:
V=Iconstant*Rreal-time
where V represents the sensed voltage, the Iconstant represents the constant current supplied by the CC driving circuit 221, and the Rreal-time represents a resistance of the NTC thermistor 21 depending on the temperature.
As shown in
The control circuitry 22 may also include a measurement circuit 222 acting as a readout circuit for the NTC thermistor 21. Here, the measurement circuit 222 can include at least one amplifier for sampling and amplifying the sensed temperature (the sensed voltage in this disclosure) output through the electrodes of the NTC thermistor 21. In an example, three stages of amplifiers (e.g., U2B OPA4330, U2C OPA4330, and U2D OPA4330) are provided in the measurement circuit 222, and a readout Vout can be amplified by those three stages of amplifiers for the convenience of transmitting or presentation.
The wireless module 25 can communicate with the control circuitry 22 to obtain the amplified voltage. A Bluetooth module (Texas Instruments CC2541) can be used as the wireless module 25 here. The readout Vout can be transferred into the wireless module 25 after amplification. A data converter 26 such as an analog to digital (A/D) converter can be further provided to communicate the control circuitry 22 with the wireless module 25 in this disclosure. After 12-bit A/D conversion, the wireless module 25 can process the converted data to generate a digital package and send out the digital package by an antenna to any other wireless reader. It is noted that although the data converter 26 is exhibited as an embedded component of the wireless module 25, the data converter 26 can also be arranged separated from the wireless module 25. Specific layout of the wireless module 25 and the data converter 26 will not limit the scope of this disclosure.
In another example, a data converter such as an analog to digital (A/D) converter can be provided to communicate the control circuitry 22 with a display component in this disclosure. After 12-bit A/D conversion, the display component can display the converted data for the user.
The above-described embodiments can provide flexible, low-cost and large-area temperature sensors which can realize fast temperature sensing due to excellent thermal insulation. Also, those temperature sensors can further be prevented from moisture penetration effectively and be kept within an allowable operation temperature under the action of the constant current driving.
For more understanding of various embodiments of the temperatures sensors in this disclosure, several examples are provided below to explain such as fabrication process, fabrication formula, material selection, sensor assembly and so on for some specific temperature sensors. Example 1 refers to a fully printable NTC thermistor produced on an 80 μm-thick PET substrate according to the design in
A fully printable NTC thermistor was produced on an 80 μm-thick PET substrate according to the design in
Formula 1 for forming the Si—C paste:
0.2 gram of diglycidyl ether of bisphenol A (DGEBA) epoxy YD-128 (supplied by Huntsman Corporation) was dissolved into 1 ml acetone by sonication for 10 min;
0.2 gram of polar Graphene powders (supplied by Angstron Materials Inc, N006-P) and 0.3 gram of Si nanopowders were added into epoxy solution by mixing in a planetary mixer (Thinky AR-100) for 2 min;
0.5 gram of Si nanopowders were further added by mixing in a planetary mixer (Thinky AR-100) for 2 min;
the addition of 0.5 g Si NPs was gradually repeated for twice and eventually a total amount of 1.8 g Si NPs were mixed with 0.2 g graphene power homogeneously into epoxy solution;
Acetone was then vaporized from the paste under fume hood for about 30 min;
1 ml analytical grade ethylene glycol (EG) was added as solvent by mixing for 2 min;
60 mg JEFFAMINE D-230 amine was added by mixing for 2 min, where the JEFFAMINE D-230 amine is a polyether diamine acted as a curing agent for epoxy YD-128, supplied by Huntsman Corporation.
EG (0.2 ml by every time) was gradually added until the viscosity is appropriate for screen printing, and the paste was defoamed for 2 min using Thinky AR-100.
Example 2In a second example, another fully printable NTC thermistor was produced according to the design in
In a third example, still another fully printable NTC thermistor was also fabricated according to the design in
In order to find suitable laminates for printed Si—C NPs sensors, properties of moisture penetration were studied for different films, including PET, PI, PET/EVA, PET/Al/EVA (a thin Al film of 3 μm), liquid crystal polymer (LCP), Al foils, Cu foils, etc. . . . The water vapor transmission rate (WVTR) was measured by MOCON 3/33MA at 38° C. 100% RH.
In a fifth example, a full assembly of a temperature sensor with a readout circuitry and a flexible lithium battery was presented according to the design shown in
According to the circuit design in
In a sixth example, another full assembly of a temperature sensor with a readout circuitry and a flexible lithium battery was also presented according to
In various embodiments and examples of this disclosure, the NTC thermistor with the LCP substrate and the hybrid laminate can be provided, such that the NTC thermistor can be prevented from the moisture from both a top and a bottom surface. In various embodiments and examples of this disclosure, the temperature sensor (especially wireless one) can be provided to have excellent thermal insulation and current control, such that the temperature sensor can sense the temperature in a faster and more accurate operation.
In various embodiments and examples of this disclosure, the NTC thermistors, the laminates, or the frames may be described to have the top surface and the bottom surface. It is noted that the terms of “top” and “bottom” are defined with respect to the human body surface to which the temperature sensor is attached. The surface facing the human body surface can be defined as the top surface, while the one facing away from the human body surface can be defined as the bottom surface; and vice versa.
In various embodiments and examples of this disclosure, the NTC thermistors, the laminates, or the frames may be described to have the front side and the back side. It is noted that the terms of “front side” and “back side” are defined with respect to the human body surface to which the temperature sensor is attached. The side facing the human body surface can be defined as the front side, while the one facing away from the human body surface can be defined as the back side.
Although the frames in the figures are shown to be a planar structure, these figures are only schematic for displaying the arrangement of the NTC thermistor, the battery and the PCBA on the frame. Alternatively, the frame may function as support the necessary components of the temperature sensor, and keep some internal components such as the PCBA and the battery from exposing to the user. Specific designs for the frame will not limit the scope of this disclosure.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to make and use the invention. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.
Many other changes and modifications may be made to this disclosure without departing from the spirit thereof. The scope of these and other changes will become apparent from the appended claims.
Claims
1. A temperature sensor based on printable thermistor, comprising:
- a negative temperature coefficient (NTC) thermistor for temperature sensing, which comprises a substrate, a Si—C film printed on the substrate, and electrodes printed on the substrate for connecting the Si—C film with a control circuitry; wherein the NTC thermistor further comprises a first laminate and a second laminate; the first laminate is directly arranged on the Si—C film and the electrodes and is configured to improve thermal curing for the NTC thermistor; the second laminate is arranged on one side of the first laminate opposite to the Si—C film and the electrodes and is configured to prevent moisture from penetrating into the NTC thermistor;
- the control circuitry which electrically connects with the NTC thermistor and operates for obtaining the temperature sensed by the NTC thermistor;
- a power source for providing power supply to the NTC thermistor and the control circuitry; and
- a frame element for supporting the NTC thermistor, the control circuitry and the power source; wherein the frame element is at least partially thermally insulated to establish thermal equilibrium within the temperature sensor.
2. The temperature sensor of claim 1, wherein the first laminate has a water vapor transmission rate (WVTR) of 1-100 gram/m2/day and the second laminate has a WVTR of below 0.1 gram/m2/day; and/or
- the first laminate is made of one selected from a group of polyethylene terephthalate, polyimide, polyethylene; and the second laminate is one selected from a group of a metal foil, a metallized polymer film, and a polymer film with a inorganic oxide coating.
3. The temperature sensor of claim 1, wherein the control circuitry comprises a constant current driving circuit which drives the NTC thermistor with a constant current, and the NTC thermistor generates a sensed voltage varying with the temperature as follows:
- V=Iconstant*Rreal-time;
- where V represents the sensed voltage, the Iconstant represents the constant current supplied by the constant current driving circuit, and the Rreal-time represents a resistance of the NTC thermistor depending on the temperature.
4. The temperature sensor of claim 3, wherein the constant current circuit comprises an operation amplifier at least one voltage sources, a first transistor and a second transistor; a first driving voltage and a second driving voltage generated by the at least one voltage sources are respectively applied to two input ends of the operation amplifier to provide a bias for the second transistor at an output end of the operation amplifier; the first transistor and the second transistor are connected into an internal feedback circuit to generate the constant current for the NTC thermistor.
5. The temperature sensor of claim 3, wherein the control circuitry further comprises a measurement circuit; the measurement circuit comprises at least one amplifier for sampling and amplifying the sensed voltage output through the electrodes of the NTC thermistor.
6. The temperature sensor of claim 5, furthering comprising a wireless module and a data converter communicated with the control circuitry; the amplified voltage is converted by the data converter to generate a data package, and the data package is transferred to the wireless module for transmitting; wherein the wireless module selects from a group comprising a Bluetooth module, a WiFi module, a Zigbee module or a radio frequency identification (RFID) module.
7. The temperature sensor of claim 1, wherein the Si—C film has a conformal contact surface for the temperature sensing, and the conformal contact surface has an area of 1-2 cm2;
- and/or,
- the substrate is a liquid-crystal-polymer (LCP) film with a WVTR of 0.01 gram/m2/day.
8. The temperature sensor of claim 1, wherein the frame element has a front side and a back side which two are configured oppositely to each other; the NTC thermistor is arranged on the front side of the frame element, and the control circuitry and the power source are arranged on the back side of the frame element;
- at least a portion of the frame element for arranging the NTC thermistor is made of polytetrafluoroethylene, polyethylene terephthalate, polypropylene, polyvinyl chloride, polyethylene or rubber; and/or a thermal insulation structure is at least disposed on the front side of the frame element corresponding to a portion of the frame element for arranging the NTC thermistor.
9. A wireless temperature sensor, comprising:
- an NTC thermistor for temperature sensing, which comprises a substrate, a sensing element, an internal laminate and an external laminate arranged successively; the sensing element comprises a Si—C film and electrodes printed on the substrate, wherein the electrodes connect the Si—C film with a control circuitry;
- the internal laminate has a WVTR of 1-100 gram/m2/day such that the NTC thermistor is provided with improved thermal curing, and the external laminate has a WVTR of below 0.1 gram/m2/day, such that the NTC thermistor is prevented from moisture penetration;
- the control circuitry, which electrically connects with the NTC thermistor and operates for obtaining the temperature sensed by the NTC thermistor; the control circuitry comprises a constant current driving circuit for driving the NTC thermistor with a constant current, and a measurement circuit for sampling a sensed voltage output through the electrodes of the NTC thermistor, wherein the sensed voltage is determined based on the constant current and a resistance of the NTC thermistor;
- a wireless module for receiving the sensed voltage from the control circuitry and sending out the sensed voltage in a wireless way;
- a power source for providing power supply to the NTC thermistor, the control circuitry and the wireless module; and
- a frame element for supporting the NTC thermistor, the control circuitry, the power source and the wireless module; wherein the frame element is at least partially thermally insulated to establish thermal equilibrium within the temperature sensor.
10. The temperature sensor of claim 1, wherein the electrodes are deposited on the substrate to form multiple pairs of fingers, and a gap is provided between each adjacent pairs of the fingers; wherein the Si—C film overlap on each gap between the fingers of the electrodes.
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Type: Grant
Filed: Nov 5, 2015
Date of Patent: Jul 31, 2018
Patent Publication Number: 20170127944
Assignee: NANO AND ADVANCED MATERIALS INSTITUTE LIMITED (New Territories)
Inventors: Caiming Sun (New Territories), Xiaohua Chen (New Territories)
Primary Examiner: Sean Dougherty
Application Number: 14/932,998
International Classification: A61B 5/00 (20060101); H01C 7/04 (20060101); G01K 1/08 (20060101); G01K 7/22 (20060101); G01K 13/00 (20060101); A61B 5/01 (20060101); H01C 1/142 (20060101); H01C 1/14 (20060101); H01C 17/28 (20060101);